The field of the invention is in a transmission device for mechanical power which has a continuously variable drive ratio. It transmits power from an input shaft at one torque and rotational speed to an output shaft at another torque and rotational speed. The ratio of input to output speeds or torques is continuously adjustable to provide any ratio in a range within limits determined by the transmission device's design.
Commercially available hydrostatic transmission devices, where typically a positive displacement variable output pump hydraulically drives a positive displacement motor, are, in many respects, superior to other approaches to variable ratio transmission such as commonly used traction drives or belt drives with variable sheave diameter. The hydrostatic transmission devices can provide a reliable positive drive with a wide drive ratio range. A major drawback, however, which has limited the application of hydrostatic transmission devices, has been their mechanical complexity and the resulting high manufacturing cost.
It is a primary object of the invention to provide a continuously variable hydrostatic mechanical power transmission device which is simple in mechanical construction.
A further object of the invention is to provide a continuously variable hydrostatic mechanical power transmission device with a wide drive ratio range.
Still further objects will become apparent upon referring to a detailed description of a preferred embodiment and the attached drawings.
The invention utilizes the variable delivery gear pump concept disclosed in U.S. Pat. No. 2,052,419 which teaches that the fluid displacement per drive gear revolution of a gear pump can be varied by the axial moving of one gear relative to the other which changes the axial length of the meshing engagement and therefore the displacement. The displacement is proportional to the axial length of the meshing engagement.